Electroplating method and electrolyte



Patented "June 22, 1948 ELECTROPLATIN G METHOD AND ELECTROLYTE Allan E. Chester, Highland Park, Ill., assignor to Poor & Company, Chicago, 111., a corporation of Delaware No Drawing. Application August 9, 1947, Serial No. 767,859

16 Claims.

This invention relates to improved electroplating baths, and more particularly to an alkaline cyanide bath or electrolyte for use in electroplating metallic surfaces at high current densities.

The present application is a continuation-inpart of my application Serial No. 450,201, filed July 8, 1942, which has become abandoned, and which was a continuation-in-part of my application Serial No. 441,694, filed May 4, 1942.

The prior art has suggested the use of calcium sulfate to control the amount of sodium carbonate formed during an electrodeposition from cyanide plating baths. This material has been added from time to time as the carbonate content has grown sufficiently high to prove harmful to the deposit or deposition rate. Brighten-- ing agents have also been added in separate operations.

One of the objects of the present invention is to provide a single additive composition which will control carbonate content in cyanide plating baths, improve the appearance and brightness of the plate, improve the cathode eiiiciency appreciably, and improve the throwing power of the bath.

Another object is to provide an electroplating bath or solution containing a substantially insoluble addition agent or additive composition which will plate fine-grained ductile deposits rapidly in a still tank.

Still a further object is to provide a plating solution containing the aforesaid substantially insoluble addition agent which may be advantageously used with an ordinary plating source of direct current voltage, but which is especially useful with plating currents of abnormal wave form such as are obtained by superimposing an alternating current component on a direct current component.

Another object of the invention is to provide an alkaline zinc cyanide plating bath which will produce bright adherent metal deposits of good quality at high electroplating rates, and in which the carbonate concentration and polarization are reduced.

These objects are accomplished in accordance with this invention by incorporating with alkaline cyanide plating baths, preferably zinc, cadmium or copper cyanide plating baths, a gluconate of an alkali metal which is slightly soluble in the cyanide plating solution and is reactive with soluble carbonates to form still more insoluble carbonates. Especially good results have been obtained with calcium gluconate or gluconate compositions containing both calcium and barium as obtained, for example, by blending barium hydroxide and calcium gluconate. The gluconate composition may function to accomplish one or more objects of the invention, depending to some extent upon the quantity used, but good results are obtained with relatively small quantities.

The invention will be illustrated but is not limited by the following examples, in which the quantities are stated in parts by weight unless otherwise indicated.

Example I An alkaline zinc cyanide bath was prepared by mixing together grams of sodium cyanide, 45 grams of zinc oxide, 15 grams of sodium hydroxide, and enough water to make a liter of solution.

To the above bath there was added one gram per liter of lauryl sulfate (sometimes called lauric alcohol sulfonate), 10 grams per liter of calcium gluconate, and one gram per liter of gum arabic. The resultant bath was continuously agitated with a rotating paddle for five or six hours until all of the ingredients had dissolved except the gluconate, which only partly dissolved.

In this bath the gum arabic assists materially in retaining the gluconate in suspension uniformly throughout the bath. The lauryl sulfate may be considered to be a wetting agent, reduc ing the surface tension and producing better deposits.

The calcium gluconate acts as a control agent for controlling the action and performance of the bath.

Example II A composition was prepared by blending together 99 pounds of barium hydroxide ground to 60 mesh and one pound of calcium gluconate.

This composition was incorporated in alkaline cyanide plating baths with agitation.

The following baths are typical plating baths to which the addition agent can be added:

A Cadmium cyanide bath 39 grams per liter of cadmium oxide (34 grams per liter of cadmium).

131 grams per liter of sodium cyanide and the remainder Water.

B. Alkaline zinc cyanide bath -100 grams sodium cyanide.

36-40 grams zinc metal (added as zinc oxide).

100-115 grams sodium hydroxide and enough water to make one liter of solution.

2 grams per liter of zinc dust were stirred into e e ct yte and t e n re m x u e was filtered in order to remove traces of heavy metal.

C. Alkaline copper cyanide bath Sodium cyanide /2 ounce to 1% ounces.

Copper cyanide-2 ounces to 4 ounces.

Sodium carbonate-2% ounces to 4% ounces.

Water in sufiicient amount to make up a gallon of bath.

To improve the general performance of any of the baths A, B and C, as little as of calcium gluconate or the equivalent quantity of the barium hydroxide calcium gluconate composition may be added to the bath. In order to effectively control the sodium carbonate content of a cyanide bath, it is desirable to use a minimum of 1.6 ounces of the barium hydroxide-calcium gluconate composition per ounce of reduction of sodium carbonate per gallon of bath, and in some cases it is desirable to use as much as 4 ounces of the barium hydroxide-calcium gluconate blend per ounce of reduction of sodium carbonate desired per gallon of bath.

As will be understood by those skilled in the art, the plating bath will tolerate a certain amount of sodium carbonate; hence, when the electrolyte is new it can be run for some time without adding .any of the gluconate composition for the specific purpose of controlling the carbonate content of the bath. On the other hand, when the carbonate content builds up to as much as 4: ounces of sodium carbonate per gallon of bath, it will usually be desirable toadd an amount of the gluconate composition effective to reduce the carbonate content. Alternatively, the gluoonate composition can be added initially or in increments from the very beginning in order to keep the bath frombuilding up an undesirable carbonate content, and at the same time to improve the performance of the bath in other respects as previously described.

A pointed out in my copending application, Serial No. 441,694,1i1ed May 4, 1942, the present invention may be applied to the electroplating of work employing an aqueous bath containing dissolved salts of the plating metal and an anode, and wherein the work is the cathode and bath soluble carbonates are formed during the electroplating operation, and the plating current applied to the cathode with respect to the anode is a pulsating direct current voltage whose instantaneous value is always positive. Excellent results have been obtained in the electroplating of work in this manner wherein the lowest instantaneous value of said pulsating voltage at the negative alternating peak is between 0.5 volt and 1.5 volts, the pulsating voltage being formed from a direct current component having a voltage not substantially higher than 24 volts, and an alternating current component having a frequency within the range of 25 to 60 cycles inclusive, while maintaining in suspension an amount of calcium gluconate of at least grams per liter of the plating bath.

It is known that the soluble carbonate content of alkaline aqueous cyanide electroplating baths can be controlled by taking the bath out of operation, cooling it and crystallizing out the carbonates. This procedure has several disadvantages, including the one that the bath must be taken out of operation for a substantial period of time. Another suggested way of controlling the carbonate content of the bath is to add calcium sulfate thereto in order to precipitate calcium carbonate. This method also has several disadvantages, one of them being that the reaction between the calcium sulfate and the soluble carbonates form soluble sulfates which are often more objectionable than the soluble carbonates. According to the present process, on the other hand, the reaction products which are left in the bath after the precipitation of the insoluble calcium carbonate are beneficial to the bath and actually increase the cathode efficiency. Another practical aspect of this invention is that the insoluble gluconates are relatively easy to filter as compared, for example, to calcium sulfate. Thus, if it becomes necessary at any time to filter the bath the operation with the present process is a relatively simple one as compared to the previously proposed use of calcium sulfate.

The invention is hereby claimed as follows:

1. The process of electrodepositing metals from an alkaline aqueous cyanide containing the plating metal in solution and wherein a bath soluble alkaline carbonate is formed during the electrodeposition which comprises incorporating with said plating solution an alkaline earth metal gluconate, the quantity of said alkaline earth metal gluconate being eifective to react with and precipitate said. bath soluble carbonate as an insoluble alkaline earth metal carbonate.

2. The process of electrodepositing metals from an alkaline aqueous cyanide containing the plating metal in solution and wherein a bath soluble alkaline carbonate is formed during the electrodeposition which comprises incorporating with said plating solution calcium gluconate, the quantity of said calcium gluconate being eilective to react with and precipitate said bath soluble carbonate as insoluble calcium carbonate.

3. The process of electrodepositing zinc from an alkaline zinc cyanide aqueous solution wherein a bath soluble alkaline carbonate is formed during the electrodeposition which comprises incorporating with said alkaline zinc cyanide aqueous solution a quantity of an alkaline earth metal gluconate, the quantity of said alkaline earth metal gluconate being effective to react with and precipitate said bath soluble carbonate as an insoluble alkaline earth metal carbonate.

e. The process of electrodepositing cadmium from an alkaline cadmium cyanide aqueous solution wherein a bath soluble alkaline carbonate is formed during the electrodeposition which comprise-s incorporating with said alkaline cadmium cyanide aqueous solution a quantity of an alkaline earth metal gluconate, the quantity of said alkaline earth metal gluconate being effective to react with and precipitate said bath soluble carbonate as an insoluble alkaline earth metal carbonate.

5. The process of electrodepositing copper from an alkaline copper cyanide aqueous solution wherein a bath soluble alkaline carbonate is formed during the electrodeposition which comprises incorporating with said alkaline copper cyanide aqueous solution a quantity of an alkaline earth metal gluconate, the quantity of said alkaline earth metal gluconate being eflective'to react tate said bath soluble carbonate as an insoluble carbonate.

'7. An alkaline aqueous cyanide plating bath electrolyte containing in solution a plating metal which forms complex cyanides and calcium gluconate, said electrolyte normally tending to form a bath soluble alkaline carbonate during electrodeposition of the plating metal and the quantity of said gluconate therein being effective to react with and precipitate said bath soluble carbonate as an insoluble carbonate.

8. An alkaline aqueous zinc cyanide plating bath containing an alkaline earth metal gluconate, said bath being characterized by the formation of a bath soluble alkaline carbonate therein during an electroplating operation and the quantity of said gluconate being effective to react with and precipitate said bath soluble carbonate as a carbonate insoluble in the bath.

9. An alkaline aqueous cadmium cyanide plating bath containing an alkaline earth metal gluconate, said bath being characterized by the formation of a bath soluble alkaline carbonate therein during an electroplating operation and the quantity of said gluconate being effective to react with and precipitate said bath soluble carbonate as a carbonate insoluble in the bath.

10. An alkaline aqueous copper cyanide plating bath containing an alkaline earth metal gluconate, said bath being characterized by the formation of a bath soluble alkaline carbonate therein during an electroplating operation and the quantity of said gluconate being effective to react with and precipitate said bath soluble carbonate as a carbonate insoluble in the bath.

11. An alkaline aqueous cyanide plating bath containing in solution a plating metal which forms complex cyanides and wherein a bath soluble alkaline carbonate is formed during an electroplating operation, and containing partially in solution an alkaline earth metal gluconate in a minimum amount of at least 1 6% by wei ht o the bath.

12. An electrolyte as claimed in claim 11 in which the gluconate is calcium gluconate.

13. In electroplating of work employing an aqueous bath containing dissolved salts of the plating metal and an anode and wherein the work is the cathode and bath soluble carbonates are formed during the electroplating operation, the method of obtaining rapid clean deposition which consists in applying to the cathode with respect to the anode a pulsating direct current voltage whose instantaneous value is always positive, and maintaining calcium gluconate as an addition agent in suspension in said bath, the quantity of said calcium gluconate being effective to react with and precipitate said bath soluble carbonates as insoluble calcium carbonate.

14. In the electrodeposition of zinc wherein sodium carbonate is formed, the step which comprises electrodepositing zinc from an aqueous sodium cyanid-zinc plating bath in the presence of calcium gluconate, the quantity of calcium gluconate being effective to react with sodium carbonate formed during the electroplating operation and to precipitate the carbonate as insoluble calcium carbonate.

15. In electroplating of work employing an aqueous alkaline zinc bath, and further employing an anode, and a cathode constituting the work, the method of obtaining rapid deposition and controlling carbonate ion concentration in the bath, which consists in applying to the cathode with respect to the anode a pulsating direct current voltage Whose instantaneous value is always positive, the lowest instantaneous value of said pulsating voltage at the negative alternating peak being between 0.5 volt and 1.5 volts, and maintaining in suspension in said alkaline zinc bath calcium gluconate in an amount of at least 10 grams per liter, said direct current component having a voltage not substantially higher than 24 volts and said alternating current component having a frequency within the range of from about 25 to cycles, inclusive.

16. In electroplating of Work employing an aqueous alkaline bath wherein an alkaline carbonate is formed, and further employing an anode, and a cathode constituting the work, the method of obtaining rapid depositon which consists in applying to the cathode with respect to the anode a pulsating direct current voltage whose instantaneous value is always positive, the lowest instantaneous value of said pulsating voltage at the negative alternating peak being between 0.5 volt and 1.5 volts, and maintaining calcium gluconate in suspension in said bath, the quantity of calcium gluconate being effective to react with sodium carbonate formed during the electroplating operation and to precipitate the carbonate as insoluble calcium carbonate.

ALLAN E. CHESTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 694,658 Meurant Mar. 4, 1902 1,388,874 Mershan Aug. 30, 1921 1,755,479 Jones Apr. 22, 1930 1,918,605 Jones July 18, 1933 2,063,760 Schulein Dec. 8, 1936 FOREIGN PATENTS Number Country Date 414,939 Great Britain Aug. 16, 1934 OTHER REFERENCES Metal Industry, Apr. 19, 1929, pp. 396-398.

Proceedings Royal Society, A112, 1926, p. 259.

Transactions Faraday Society, vol. 18, 1922, p. 102; vol. 24, 1928, pp. 348-358. 

